Tropomyosin (Tm) is modified by both posphorylation and nitration post-translational modifications. To date tiie functional significance of Tm pfiospliorylation and nitration are not well understood. It is the goal of this proposal to identify the effect of Tm phosphorylation and nitration on its interactions with the sarcomeric proteins and on activation of the sarcomeric thin filament. Recent data has suggested the post-transiational modification of Tm may be regulated, therefore we further propose to investigate the effect of cardiac stress on the level of Tm post-translational modifications as a novel signaling mechanism to alter cardiac sarcomeric contraction. This application contains three specific aims to investigate these questions. 1) Does cardiac stress alter the post-tranlational modification of Tm to affect contractile function? 2) Does the posttranslational modification of Tm by phsophorylation or nitration alter its interactions within the thin filament protein network? 3) Do post-transiational modifications of Tm alter Ca2+ activation of the thin filament? These aims wiil be carried out by investigating the effect of Tm that has been modified by either phosphorylation or nitration on Tm binding affinity to the other sarcomeric thin filament proteins, the binding of Ca2+ and the ATPase activity of reconstituted thin filaments. We also propose to investigate the effect of cardiac stress on Tm post-translational modifications by treating cardiac myocytes with ischemic reperfusion followed by identification of Tm phosphorylation and nitration levels. We will investigate the significance of Tm phosphorylation by investigating calcium regulated force development in cardiac fibers from transgenic mice overexpressing pseudo-phosphorylated Tm. These studies will provide a much needed molecular understanding of how the post-translaitonal modification of Tm functions to affect cardiac contraction at the sarcomeric level and its role as a novel signaling mechanism to affect cardiac contraction in ischemic reperfusion. The findings from these studies are direclty relevant to understanding the molecular basis of cardiac dysfunction in human myocardial infarction. These studies wiil also provide new insight into potential pharmacotheriputic treatments to improve heart function in both myocardial infarction and disease.